Ion-assisted deposition of coatings on various substrates is well known. An excellent discussion of related processes is found in the article “Plasma and Ion Sources In Large Area Coatings: A Review”, published by the Lawrence Berkley National Laboratory, University of California, based on a paper presented at the International Conference on Metallurgical Coatings and Thin Films in 2005, by Dr. Andre Anders.
Particularly challenging problems arise in efforts to conduct ion-assisted deposition on large substrates, such as plate glass. Glass is typically manufactured in 12 foot or wider formats. Since glass is a non-conductive substrate, it does not readily conform itself to the use of conventional bias generators to modify film structure during sputter coating operations.
In the present state of the art, the coating material is typically generated with magnetrons having generally planar configurations or rotating cylinder configurations. However, the arriving plasma stream generated with these types of magnetrons is composed of weakly charged ions and atoms.
Numerous attempts have been made to use current off the shelf closed drift anode layer linear ion technologies to provide a means of ion assist during the production of plate glass, but without success. Current linear design ion sources are designed to run at high voltages, typically 1500-3000 volts in a linear collimated beam format, although the same sources can be run in a “diffuse mode” where the voltage ranges are considerably lower. However, when operating in the diffuse mode, the plasma is very dense and approaches an electrically neutral charge state. This process requires relatively high gas pressures, and the high gas flow is required for diffuse mode operation are typically not compatible with the finely tailored gas flow desired.
In collimated beam format, a preferred format for effective ion assist, as compared to the above-described diffuse mode, there are severe limitations present with current linear ion sources. Specifically, high voltages are required in the collimated beam format, and such high voltages impart substantially higher energies to the departing ions, often destroying the sputtered film at a faster rate than it can condense. These processes utilizing high voltages and high current are well suited for ion etching and pre-treating of substrates in many cases, but are not effective for ion-assisted deposition.
The current ion source technology is also restricted in the optimal pressure range. For example, linear ion sources of the anode layer type such as those provided by the Advanced Energy Corporation, are typically recommended for operation in pressure ranges deeper than 1 mTorr. This pressure range is outside of the preferred sputtering ranges used in the industry. As sputtering pressure becomes deeper and deeper, the deposition rate is severely handicapped, which slows the building rate of the film thickness, and thus leads to increased production times.
It would be desirable to have an ion source that is capable of operating over a broader range of pressures than previously known ion sources, while at the same time operating at voltages that are greatly reduced compared to previously known ion sources.